It has long been known that a rotating flexible disc used for recording or reading of indicia thereon must be stabilized at the precise point where the indicia is recorded or read. This is particularly acute when the rotating disc is a disc bearing optical signals such as video signals. With such devices, the disc must be stabilized during the specific point of reading thereby to assure that the recorded indicia is within the optical depth of field required by the optical apparatus employed.
Apparatus of the type herein involved typically utilizes a flexible disc which is rotated at a relatively high speed over a base plate or similar device and within a hydrodynamic fluid such as air. The air acts as a cushion or bearing for the rotating disc or alternatively functions as a laminar layer of air through which the disc rotates. In either instance, the disc is supported above the base plate by a layer or cushion of air and there is no particular support or plate above the rotating disc.
Various stabilization devices are known to the prior art. One such device is disclosed in French Patent 2,209,981, published July 5, 1974 for "Air Cushion Bearing for Optical Systems" in which a reading head containing a nozzle through which air is forced is maintained at a fixed distance from a rigid surface by being balanced with a mechanical force which draws the head toward the surface.
Another such device is disclosed in U.S. Pat. No. 2,905,768 which again utilizes air ejected through two sets of openings to form an air cushion bearing between a planar face on the reading head and the surface of the rotatin disc.
A further such device is shown in U.S. Pat. No. 3,166,997 wherein nozzles are spaced on each side of the rotating disc and air cushion bearings are formed by air being passed through the nozzles.
U.S. Pat. No. 3,914,541 discloses a different device in which the rotating disc is positioned above a reference surface or turntable and the reading head comprises a chamber to which is applied a reduced pressure generating an air delivery which attracts the zone of the disc located in the proximity of the nozzle.
A still further device is shown in U.S. Pat. No. 4,071,854 which employs the force of attraction of a Bernouilli force acting on the zone of the rotating disc opposite a nozzle which ejects fluid under pressure so as to attract that portion of the disc located immediately beneath the nozzle.